The present invention relates to a process and to an apparatus making it possible to treat on the surface and in depth a material by a thermoionic effect with a view to modifying its physicochemical properties.
It more particularly applies in the filed of metallurgy to the modification of mechanical properties, both on the surface and in depth, of metals or alloys (reducing the friction coefficient, increasing the resistance to shock, wear, ablation, etc) or for modifying the chemical properties of these materials (corrosion resistance).
However, the invention also applies to the field of microelectronics for modifying the electrical properties of semiconductors and in the field of integrated optics for modifying the refractive indices of certain materials.
The invention also applies both to the treatment of a material partly forming the outer wall of a hollow or solid member and to the treatment of a material partly forming the inner wall of a hollow member.
It is presently known to use the ion implantation of certain chemical species into the surface layer of certain metals in order to modify the mechanical surface properties thereof.
In particular, it is known to produce a surface alloy by implanting ions in a material. This surface production of an alloy is more particularly described in the article in Thin Solid Films, 96, 1982, pp 31-44, Metallurgical and protective coatings by S. WEISSMANTEL et al entitled "Preparation and properties of hard i-C and i-BN coatings". Unfortunately, the implantation of ions in a material considerably increases the thermal stressing of the material, so that its corrosion resistance is reduced.
Moreover, it is known from U.S. Pat. No. 4,398,966, published on Aug. 16, 1983, to increase the corrosion resistance of a steel by subjecting its surface to pulsed laser radiation. Laser impact on the steel surface produces high local heating which stops at the same time as the laser pulse stops. This corresponds to a surface hardening or transient annealing phenomenon used for blocking the structure of the steel obtained at high temperature.
It is also known to use a pulsed laser beam for vaporizing a material, whereby the vaporized material can then be deposited in the form of thin films on a support. This thin film deposition procedure is more particularly described in an article by J. DESSERRE and J. F. ELOY which appeared in B.I.S.T. C.E.A, No. 204, June 1975 and entitled in translation "Interaction of a pulsed coherent light beam with a complex target and application to the production of thin film compounds."
The vaporization of a material with a view to its deposition can in particular be carried out by irradiating a block of said material through a substrate which is optically transparent to the laser radiation used. Such a process is particularly described in No. EP-A-0 002 738.
Moreover, it is known to modify the surface mechanical properties of a material by irradiating it with laser radiation through a substrate, the latter being optically transparent to said radiation. Such a process is described in U.S. Pat. No. 4,401,477, published on Aug. 30, 1983.
In this process, the surface of the material to be treated is covered with a layer absorbing the laser photons with a view to increasing the absorption of the laser radiation by the material to be treated. The laser used is a high power pulsed laser.
The deposition of said absorbing layer of photons requires a particular surface state for the member to be treated, which increases the material treatment time. In addition, this treatment process requires the use of a compression chamber.